Long-term White Spruce Branch Primary Growth (Agashashok River, Alaska, 2010-2025)

The Arctic is warming much faster than the rest of the globe and the warming is seasonally asymmetrical, with modest warming during the summer months and extreme warming during the winter months. In many regions of the Arctic, extreme winter warming is coupled with observed and projected increases in winter precipitation. The combination of extreme winter warming and increasing winter precipitation will lead to rapid winter soil warming, with wide ranging consequences for ecosystem function. Warmer winter soils are generally associated with greater overwinter microbial activity, enhanced breakdown of soil organic matter and a flush of nutrients that may be available for plant uptake following snowmelt. Our long-term research near the Arctic treeline in the western Brooks Range of Alaska has revealed the potential importance of deeper snowpacks and warmer winter soils for the productivity of treeline trees and their advance into the tundra. Here, we present long-term (2010-2025) annual measurements of white spruce branch primary growth at three sites (terrace, forest, treeline) in the Agashashok River watershed, Noatak National Preserve, northwest Alaska. Measurements were made on two branches on each of 10 control trees at breast height using calipers in the field. Detailed site descriptions are available in Sullivan, P. F., Ellison, S. B., McNown, R. W., Brownlee, A. H., &Sveinbjörnsson, B. (2015). Evidence of soil nutrient availability as the proximate constraint on growth of treeline trees in northwest Alaska. Ecology, 96(3), 716-727. These are the same 10 control trees at each site described in our Ecology article.